1、 IEC TR 62316 Edition 3.0 2017-07 TECHNICAL REPORT Guidance for the interpretation of OTDR backscattering traces for single-mode fibres IEC TR 62316:2017-07(en) colour inside THIS PUBLICATION IS COPYRIGHT PROTECTED Copyright 2017 IEC, Geneva, Switzerland All rights reserved. Unless otherwise specifi
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10、ish to give us your feedback on this publication or need further assistance, please contact the Customer Service Centre: csciec.ch. IEC TR 62316 Edition 3.0 2017-07 TECHNICAL REPORT Guidance for the interpretation of OTDR backscattering traces for single-mode fibres INTERNATIONAL ELECTROTECHNICAL CO
11、MMISSION ICS 33.180.10 ISBN 978-2-8322-4553-8 Registered trademark of the International Electrotechnical Commission Warning! Make sure that you obtained this publication from an authorized distributor. colour inside 2 IEC TR 62316 IEC 2017 CONTENTS FOREWORD . 4 1 Scope 6 2 Normative references 6 3 T
12、erms and definitions 6 4 Backscattering phenomenon 6 4.1 Rayleigh scattering . 6 4.2 Fresnel reflections and dead zone fibres . 6 5 Measurement of the backscattered power (OTDR) . 7 5.1 General . 7 5.2 Representation of the backscattered power. 7 5.3 Noise and perturbations 8 6 Interpretation of a b
13、ackscattering trace 8 6.1 General . 8 6.2 Launch cord 9 6.3 Tail cord . 9 6.4 Unidirectional trace . 9 6.4.1 General . 9 6.4.2 Slope as the attenuation coefficient of a fibre 10 6.4.3 Impurity and discontinuity 10 6.4.4 Pulse width 10 6.4.5 Polarization effects 10 6.5 Bi-directional trace 11 6.5.1 G
14、eneral . 11 6.5.2 Attenuation uniformity 11 6.5.3 MFD uniformity 12 6.6 Splice loss evaluation . 12 6.6.1 General . 12 6.6.2 Event measurement methods . 13 6.6.3 Apparent losers and gainers 14 6.6.4 Example of apparent splice loss evaluation for uni-directional OTDR measurements . 17 7 Uncertainties
15、, deviation and resolution 18 7.1 General . 18 7.2 Attenuation coefficient measurements . 18 7.3 Fault locations 19 Bibliography 21 Figure 1 Unidirectional OTDR trace showing splice and/or macro bend loss. 9 Figure 2 Idealized unidirectional OTDR traces corresponding to a non-reflective splice betwe
16、en two fibres 13 Figure 3 OTDR traces for similar or different fibre types with different MFD and/or different backscatter properties . 14 Figure 4 Loss in unidirectional OTDR measurements as function of the MFD difference between two spliced fibres 15 IEC TR 62316 IEC 2017 3 Figure 5 Theoretical po
17、wer through splice loss due to MFD difference (with 1= 9m) . 16 a) Mean spice loss measured from B6 to B1.3 fibre 17 b) Mean spice loss measured from B1.3 to B6 fibre 18 Figure 6 Apparent cumulative unidirectional backscattering mismatch distribution for six splice combinations of B1.3 and B6 report
18、ed in Table 1 . 18 Figure 7 Schematic drawing of a fibre with two consecutive defects 1 and 2 19 Table 1 Summary for six fibre splice combinations of B1.3 and B6 based on popular 1 310 nm MFD fibre distributions 17 4 IEC TR 62316 IEC 2017 INTERNATIONAL ELECTROTECHNICAL COMMISSION _ GUIDANCE FOR THE
19、INTERPRETATION OF OTDR BACKSCATTERING TRACES FOR SINGLE-MODE FIBRES FOREWORD 1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising all national electrotechnical committees (IEC National Committees). The object of IEC is to promote internati
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30、ernational Standards. However, a technical committee may propose the publication of a Technical Report when it has collected data of a different kind from that which is normally published as an International Standard, for example “state of the art“. IEC TR 62316, which is a Technical Report, has bee
31、n prepared by subcommittee 86A: Fibres and cables, of IEC technical committee 86: Fibre optics. This third edition cancels and replaces the second edition published in 2007. It constitutes a technical revision. This edition includes the following significant technical changes with respect to the pre
32、vious edition: a) the scope has been extended to include single-mode fibres; a) backscattered power effects are discussed in case of unidirectional trace, including so-called losers and gainers. b) example of apparent splice loss evaluation for unidirectional OTDR measurements has been added: IEC TR
33、 62316 IEC 2017 5 c) description of launch and tail cords have been added; d) figures have been improved. The text of this Technical Report is based on the following documents: Enquiry draft Report on voting 86A/1754/DTR 86A/1768A/RVC Full information on the voting for the approval of this technical
34、 report can be found in the report on voting indicated in the above table. This document has been drafted in accordance with the ISO/IEC Directives, Part 2. The committee has decided that the contents of this document will remain unchanged until the stability date indicated on the IEC website under
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36、s publication indicates that it contains colours which are considered to be useful for the correct understanding of its contents. Users should therefore print this document using a colour printer. 6 IEC TR 62316 IEC 2017 GUIDANCE FOR THE INTERPRETATION OF OTDR BACKSCATTERING TRACES FOR SINGLE-MODE F
37、IBRES 1 Scope IEC 62316, which is a Technical Report, aims to provide guidelines for the interpretation of backscattering traces, as obtained by traditional optical time domain reflectometers (OTDRs) not including polarization OTDRs for single-mode fibres. Also, backscattered power effects are discu
38、ssed in case of unidirectional trace. Full description of the test measurement procedure can be found in Annex C of IEC 60793-1-40:2001. 2 Normative references There are no normative references in this document. 3 Terms and definitions No terms and definitions are listed in this document. ISO and IE
39、C maintain terminological databases for use in standardization at the following addresses: IEC Electropedia: available at http:/www.electropedia.org/ ISO Online browsing platform: available at http:/www.iso.org/obp 4 Backscattering phenomenon 4.1 Rayleigh scattering Rayleigh scattering or backscatte
40、ring originates from fluctuations in the density, and hence in the index of refraction, of the material constituting the wave-guide; optical fibres are made of amorphous silica, and density fluctuations are a consequence of the manufacturing process. 4.2 Fresnel reflections and dead zone fibres When
41、 a light ray reaches a surface at an angle of incidence from the normal to that surface and that surface separates two media of different index of refraction, part of this light ray is refracted in the second medium and part of it is reflected backward into the first medium. This is the Fresnel refl
42、ection, which can be very high, depending on the difference in the index of refraction of the two media, on the aspect of the surface, the surface roughness, the angle of incidence and the surface defects. In most situations, strong Fresnel reflections cause non-linearities at the receiver. These no
43、n-linearities can overload the receiver resulting in signal clipping, pulse widening, tailing, and ghosts. The corresponding section of the optical time domain reflectometer (OTDR) trace following the intense Fresnel reflection defines the deadzone. This particular deadzone should not be confused wi
44、th the manufacturers specification, always defined with a narrow pulse and small Fresnel reflection. The effect of the strong reflection on the deadzone is usually resolved by cleaning the connector responsible for the reflection. The so-called deadzone eliminator (adding a length of fibre after a s
45、trong reflection) does not reduce the deadzone nor the strong reflection. It artificially moves the virtual bulkhead connector to another location and assumes the following connector has a low reflection. Depending on the type of photodetector used in the receiver, the tailing due to a strong reflec
46、tion can be greater than the fibre length inserted between the OTDR and the fibre under test. IEC TR 62316 IEC 2017 7 5 Measurement of the backscattered power (OTDR) 5.1 General The power backscattered by an optical fibre is measured by means of OTDRs. They are based on the principle of sending one
47、pulse or typically a train of pulses from one fibre end, and measure the power back-reflected from the fibre at the same end. In OTDR traces, space and time are completely equivalent through the relation: ) ( g n c t z =(1) where z is the distance (in meters); t is the time (in seconds); c is the sp
48、eed of light in vacuum (299 792 458 meters/second); n gis the group index of refraction (as a function of the wavelength). The group index of refraction, to be supplied by the fibre manufacturer, takes into account the wave-guiding properties of the fibre and the different materials used for the cla
49、dding and the core. It also adjusts the speed of light in the studied material. The group index of refraction n gis related to the phase index n or n p(which is measured on a fibre and its fundamental attribute) by using the following expression: d dn n n p p g = (2) 5.2 Representation of the backscattered power A possible schematic representation of the OTDR power P(z) at wavelength backscattered by a point z along an optical fibre is: ( ) z P z C z P 10 2 w i 2 2 10 ) ( )
